Past and projected future changes in snowpack and soil frost at the Hubbard Brook Experimental Forest,New Hampshire,USA

Long‐term data from the Hubbard Brook Experimental Forest in New Hampshire show that air temperature has increased by about 1 °C over the last half century. The warmer climate has caused significant declines in snow depth, snow water equivalent and snow cover duration. Paradoxically, it has been suggested that warmer air temperatures may result in colder soils and more soil frost, as warming leads to a reduction in snow cover insulating soils during winter. Hubbard Brook has one of the longest records of direct field measurements of soil frost in the United States. Historical records show no long‐term trends in maximum annual frost depth, which is possibly confounded by high interannual variability and infrequency of major soil frost events. As a complement to field measurements, soil frost can be modelled reliably using knowledge of the physics of energy and water transfer. We simulated soil freezing and thawing to the year 2100 using a soil energy and water balance model driven by statistically downscaled climate change projections from three atmosphere‐ocean general circulation models under two emission scenarios. Results indicated no major changes in maximum annual frost depth and only a slight increase in number of freeze–thaw events. The most important change suggested by the model is a decline in the number of days with soil frost, stemming from a concurrent decline in the number of snow‐covered days. This shortening of the frost‐covered period has important implications for forest ecosystem processes such as tree phenology and growth, hydrological flowpaths during winter, and biogeochemical processes in soil. Published in 2010 by John Wiley & Sons, Ltd.     

Evaluation of forest disturbance legacy effects on dissolved organic matter characteristics in streams at the Hubbard Brook Experimental Forest,New Hampshire

Dissolved organic matter (DOM) source and composition are critical drivers of its reactivity, impact microbial food webs and influence ecosystem functions. It is believed that DOM composition and abundance represent an integrated signal derived from the surrounding watershed. Recent studies have shown that land-use may have a long-term effect on DOM composition. Methods for characterizing DOM, such as those that measure the optical properties and size of the molecules, are increasingly recognized as valuable tools for assessing DOM sources, cycling, and reactivity. In this study we measured DOM optical properties and molecular weight determinations to evaluate whether the legacy of forest disturbance alters the amount and composition of stream DOM. Differences in DOM quantity and composition due to vegetation type and to a greater extent, wetland influence, were more pronounced than effects due to disturbance. Our results suggest that excitation-emission matrix fluorescence with parallel factor analysis is a more sensitive metric of disturbance than the other methods evaluated. Analyses showed that streams draining watersheds that have been clearcut had lower dissolved organic carbon (DOC) concentrations and higher microbially-derived and protein-like fluorescence features compared to reference streams. DOM optical properties in a watershed amended with calcium, were not significantly different than reference watersheds, but had higher concentrations of DOC. Collectively these results improve our understanding of how the legacy of forest disturbances and natural landscape characteristics affect the quantity and chemical composition of DOM in headwater streams, having implications for stream water quality and carbon cycling.     

Landscape influences on aluminium and dissolved organic carbon in streams draining the Hubbard Brook valley,New Hampshire,USA

Concentrations of both aluminium (Al) and dissolved organic carbon (DOC) in stream waters are likely to be regulated by factors that influence water flowpaths and residence times, and by the nature of the soil horizons through which waters flow. In order to investigate landscape‐scale spatial patterns in streamwater Al and DOC, we sampled seven streams draining the Hubbard Brook valley in central New Hampshire. We observed considerable variation in stream chemistry both within and between headwater watersheds. Across the valley, concentrations of total monomeric aluminium (Al_m) ranged from below detection limits (<0·7 µmol l⁻¹) to 22·3 µmol l⁻¹. In general, concentrations of Al_m decreased as pH increased downslope. There was a strong relationship between organic monomeric aluminium (Al_o) and DOC concentrations (R² = 0·92). We observed the highest Al_m concentrations in: (i) a watershed characterized by a steep narrow drainage basin and shallow soils and (ii) a watershed characterized by exceptionally deep forest floor soils and high concentrations of DOC. Forest floor depth and drainage area together explained much of the variation in ln Al_m (R² = 0·79; N = 45) and ln DOC (R² = 0·87; N = 45). Linear regression models were moderately successful in predicting ln Al_m and ln DOC in streams that were not included in model building. However, when back‐transformed, predicted DOC concentrations were as much as 72% adrift from observed DOC concentrations and Al_m concentrations were up to 51% off. This geographic approach to modelling Al and DOC is useful for general prediction, but for more detailed predictions, process‐level biogeochemical models are required. Copyright © 2005 John Wiley & Sons, Ltd.     

Watershed studies at the Hubbard Brook Experimental Forest: Building on a long legacy of research with new approaches and sources of data

The Hubbard Brook Experimental Forest (HBEF) was established in 1955 by the U.S. Department of Agriculture, Forest Service out of concerns about the effects of logging increasing flooding and erosion. To address this issue, within the HBEF hydrological and micrometeorological monitoring was initiated in small watersheds designated for harvesting experiments. The Hubbard Brook Ecosystem Study (HBES) originated in 1963, with the idea of using the small watershed approach to study element fluxes and cycling and the response of forest ecosystems to disturbances, such as forest management practices and air pollution. Early evidence of acid rain was documented at the HBEF and research by scientists at the site helped shape acid rain mitigation policies. New lines of investigation at the HBEF have built on the long legacy of watershed research resulting in a shift from comparing inputs and outputs and quantifying pools and fluxes to a more mechanistic understanding of ecosystem processes within watersheds. For example, hydropedological studies have shed light on linkages between hydrologic flow paths and soil development that provide valuable perspective for managing forests and understanding stream water quality. New high frequency in situ stream chemistry sensors are providing insights about extreme events and diurnal patterns that were indiscernible with traditional weekly sampling. Additionally, tools are being developed for visual and auditory data exploration and discovery by a broad audience. Given the unprecedented environmental change that is occurring, data from the small watersheds at the HBEF are more relevant now than ever and will continue to serve as a basis for sound environmental decision-making.     

Comparison of the water balance for an undeveloped and a suburban catchment

Abstract

Two topographically similar adjacent catchments near Johannesburg, South Africa, one suburban, the other natural grassland, were monitored over a five year period to detect differences in runoff and hydrological balance. A network of raingauges, boreholes, flow gauges and water meters was installed. Evapotranspiration was modelled using observed weather data. Groundwater was estimated from tracer and other borehole tests. Surface runoff from the undeveloped and suburban catchments was 4% and 15% of rainfall respectively. Evapotranspiration was 63% of rainfall for both catchments. Sewage outflow was 83% of water consumption for the suburban catchment. Little change in water table level occurred in the suburban catchment, and garden watering probably balanced the high evaporation. Piped water supply was 16% of the precipitation on the catchment.     

Vegetation characteristics and the prediction of runoff: Analysis of an experiment in the New Forest,Hampshire

Vegetation characteristics have not been sufficiently utilized in catchment runoff models. An analysis of storm hydrograph data from nested subareas of the Highland Water catchment, New Forest, U.K., indicates that depth of runoff and peak discharge from areas under heathland cover is substantially greater than from areas under woodland cover at several spatial scales. The significance of heath vegetation composition in the identification of runoff contributing areas is illustrated by an analysis of vegetation composition, water table depth, baseflow discharge and storm runoff from areas predominantly covered by heathland. Methods are proposed to employ the hydrological characteristics of heathland to refine and develop the Flood Studies Approach to discharge estimation in ungauged heathland catchments. Such an approach is greatly facilitated by the use of remotely-sensed data.     

Simulation of water balance and forest treatment effects at the H.J. Andrews Experimental Forest

The distributed hydrology soil–vegetation model (DHSVM) was applied to the small watersheds WS1, 2, 3 in H.J. Andrews Experimental Forest, Oregon, and tested for skill in simulating observed forest treatment effects on streamflow. These watersheds, located in the rain–snow transition zone, underwent road and clearcut treatments during 1959–66 and subsequent natural regeneration. DHSVM was applied with 10 m and 1 h resolution to 1958–98, most of the period of record. Water balance for old‐growth WS2 indicated that evapotranspiration and streamflow were unlikely to be the only loss terms, and groundwater recharge was included to account for about 12% of precipitation; this term was assumed zero in previous studies. Overall efficiency in simulating hourly streamflow exceeded 0·7, and mean annual error was less than 10%. Model skill decreased at the margins, with overprediction of low flows and underprediction of high flows. However, statistical analyses of simulated and observed peakflows yielded similar characterizations of treatment effects. Primary simulation weaknesses were snowpack accumulation, snowmelt under rain‐on‐snow conditions, and production of quickflow. This was the first test of DHSVM against observations of both control and treated watersheds in a classic paired‐basin study involving a long time period of forest regrowth and hydrologic recovery. Copyright © 2005 John Wiley & Sons, Ltd.     

On the validation of a coupled water and energy balance model at small catchment scales

Catchment runoff is the most widely used catchment scale measurement in modelling studies, and we have a reasonable degree of confidence in its accuracy. The advent of satellites gives access to a new suite of measurements taken over a defined spatial range. These measurements, principally reflected or emitted radiation, provide hydrologists with new possibilities for quantifying the state of a catchment. Surface temperatures can be readily measured by a satellite on a scale comparable to the size of a small catchment.

In this paper we show that satellite sensed temperatures can provide an important measure of catchment status, which can complement runoff measurements in water balance studies. A one-dimensional model, which couples the land surface energy balance with the soil and surface water balance is tested by comparison with runoff and with remotely sensed surface temperature measurements. Simulations have been run over four years for two small catchments which have a fairly homogeneous vegetation, one being forest and its neighbour pasture. Satellite “surface” temperatures have been interpreted in terms of the energy balance, and used as a test of modelling accuracy. An “effective” surface temperature is calculated as a weighted mean of temperatures of the separate soil and leaf surfaces. This modelled “effective” temperature correlates well with Landsat TM surface temperatures.

When pasture replaces forest, the model predicts a reduction in evapotranspiration of around 30%, a three-fold increase in runoff, and an increase in mean soil moisture status. The change to pasture also results in a rise in mean effective surface temperature of about 4°C, and an increase in summer diurnal temperature range from 10 to 22°C. The winter diurnal temperature range is similar for both vegetation systems.

Inclusion of soil moisture variability in thermal properties results in an increase in mean daily maximum temperature of about 2°C in summer and winter, without much change in daily minima. The daily mean temperature is not significantly affected.     

Hydrological and meteorological data from research catchments at the Marcell Experimental Forest,Minnesota, USA

The Marcell Experimental Forest (MEF) in northern Minnesota, USA, with hydrological research and monitoring of peatland catchments in a low-topographic relief landscape, contrasts with the mountainous terrain that typifies most research catchments. Six research catchments were instrumented and hydrological and meteorological monitoring was initiated during 1960. Paired-catchment studies, which started during 1969, have been used to assess land management and environmental change effects on forests, water availability, and biogeochemistry. Over the decades, the research and collaborations have proliferated to include new monitoring and ecosystem experiments. We provide an overview of available datasets and access information for hydrological and meteorological data. Data on streamflow, water table elevation, precipitation, snow, ground frost, air temperature, soil moisture, upland runoff, and water chemistry are discoverable with associated metadata and are archived through several Web-based, community repositories. The research programme is ongoing and we anticipate updates on an annual or more frequent basis. Additionally, we aim to release other physical, chemical, and isotopic measurements associated with long-term catchment monitoring and studies at the MEF.     

Stormflow generation in a small rainforest catchment in the Luquillo Experimental Forest,Puerto Rico

Various complementary techniques were used to investigate the stormflow generating processes in a small headwater catchment in northeastern Puerto Rico. Over 100 samples were taken of soil matrix water, macropore flow, streamflow and precipitation, mainly during two storms of contrasting magnitude, for the analysis of calcium, magnesium, silicon, potassium, sodium and chloride. These were combined with hydrometric information on streamflow, return flow, precipitation, throughfall and soil moisture to distinguish water following different flow paths. Geo‐electric sounding was used to survey the subsurface structure of the catchment, revealing a weathering front that coincided with the elevation of the stream channel instead of running parallel to surface topography. The hydrometric data were used in combination with soil physical data, a one‐dimensional soil water model (VAMPS ) and a three‐component chemical mass‐balance mixing model to describe the stormflow response of the catchment. It is inferred that most stormflow travelled through macropores in the top 20 cm of the soil profile. During a large event, saturation overland flow also accounted for a considerable portion of the stormflow, although it was not possible to quantify the associated volume fully. Although the mass‐balance mixing model approach gave valuable information about the various flow paths within the catchment, it was not possible to distill the full picture from the model alone; additional hydrometric and soil physical evidence was needed to aid in the interpretation of the model results. Copyright © 2004 John Wiley & Sons, Ltd.     

Evidence for influence of mineral weathering on stream water sulphate in Vermont and New Hampshire (USA)

Mass balance studies in forested catchments in the northeastern USA show that S losses via streamwater SO₄^2? exceed measured atmospheric S inputs. Possible sources of the excess S loss include underestimated dry deposition, mineralization of organic S in soils, desorption of soil sulphate, oxidation of recently formed sulphides and mineral weathering. Evaluating the relative contribution of these sources and processes to SO₄^2? export is important to our understanding of S cycling as well as to policy makers in their evaluation of the efficacy of S emission controls. In order to evaluate the potential for mineral weathering contributions to SO₄^2? export, we measured concentration and isotopic composition (δ³⁴S and δ¹⁸O) of SO₄^2? in stream water, and concentration and δ³⁴S values of four S fractions in bedrock and soil parent material in catchments of varying geological composition. Geological substrates with low S concentrations were represented by catchments underlain by quartzite and granite, whereas geological substrates with high S concentrations were represented by catchments underlain by sulphidic slate, schist and metavolcanic rocks. Catchments with S‐poor bedrock had stream‐water SO₄^2? concentrations <100 µeq L^?1 and isotopic values consistent with those of atmospheric SO₄^2? that had been cycled through the organic soil pool. Catchments with S‐rich bedrock had stream‐water SO₄^2? concentrations ranging from 56 to 229 µeq L^?1. Isotopic values deviated from those of SO₄^2? in atmospheric deposition, clearly indicating a mineral weathering source in some cases, whereas in others spatial variability of mineral δ³⁴S values precluded the isotopic detection of a weathering contribution. These results, along with evidence suggesting formation of secondary sulphate minerals in bedrock weathering rinds, indicate that mineral weathering may be an important source of S in the surface waters of some forested catchments in the northeastern USA. Copyright © 2004 John Wiley & Sons, Ltd.     

The effect of terrace geology on ground‐water movement and on the interaction of ground water and surface water on a mountainside near Mirror Lake,New Hampshire,USA

The west watershed of Mirror Lake in the White Mountains of New Hampshire contains several terraces that are at different altitudes and have different geologic compositions. The lowest terrace (FSE) has 5 m of sand overlying 9 m of till. The two next successively higher terraces (FS2 and FS1) consist entirely of sand and have maximum thicknesses of about 7 m. A fourth, and highest, terrace (FS3) lies in the north‐west watershed directly adjacent to the west watershed. This highest terrace has 2 m of sand overlying 8 m of till. All terraces overlie fractured crystalline bedrock. Numerical models of hypothetical settings simulating ground‐water flow in a mountainside indicated that the presence of a terrace can cause local ground‐water flow cells to develop, and that the flow patterns differ based on the geologic composition of the terrace. For example, more ground water moves from the bedrock to the glacial deposits beneath terraces consisting completely of sand than beneath terraces that have sand underlain by till. Field data from Mirror Lake watersheds corroborate the numerical experiments. The geology of the terraces also affects how the stream draining the west watershed interacts with ground water. The stream turns part way down the mountainside and passes between the two sand terraces, essentially transecting the movement of ground water down the valley side. Transects of water‐table wells were installed across the stream's riparian zone above, between, and below the sand terraces. Head data from these wells indicated that the stream gains ground water on both sides above and below the sand terraces. However, where it flows between the sand terraces the stream gains ground water on its uphill side and loses water on its downhill side. Biogeochemical processes in the riparian zone of the flow‐through reach have resulted in anoxic ground water beneath the lower sand terrace. Results of this study indicate that it is useful to understand patterns of ground‐water flow in order to fully understand the flow and chemical characteristics of both ground water and surface water in mountainous terrain. Copyright © 2007 John Wiley & Sons, Ltd.     

Sources and biodegradability of dissolved organic matter in two headwater peatland catchments at the Marcell Experimental Forest,northern Minnesota,USA

Where they are present in catchments, peatlands are a dominant source of dissolved organic matter (DOM) to surrounding waterways due, in part, to high production rates. Despite the preponderance of peatlands in northern latitudes and expected peatland vulnerability to climate change, little is known about peatland DOM degradation relative to a more comprehensive understanding of degradation when DOM is sourced from upland-dominated catchments. We compared DOM biodegradability of various sources of stream water in two catchments having peatlands (22%–33% of the area) surrounded by upland forests (70%–90% of the area, either deciduous or coniferous). We measured total organic carbon (TOC), and biodegradable dissolved organic carbon concentrations; bacterial respiration rates; streamflow; and upland runoff during and after snowmelt (March to June, 2009–2011). We also explored if DOM in upland runoff stimulated biodegradation of peatland-derived DOM (i.e., a priming effect), and if forest cover type affected DOM biodegradability. As expected, the peatlands were the largest sources of both water (72%–80%) and TOC (92%–96%) to the streams although more area in each catchment was in uplands (70%–90%). Several results were unexpected, yet revealing: (1) DOM from peatlands sometimes had the same biodegradability as DOM from uplands, (2) upland sources of DOM had negligible effects on biodegradability in the peatland and downstream, and (3) upland deciduous cover did not yield more degradable DOM than conifer cover. The most pronounced effect of upland runoff was dilution of downstream TOC concentrations when there was upland runoff. Overall, the effects of upland DOM may have been negligible due to the overriding effect of the large amount of biodegradable DOM that originated in bogs. This research highlights that peatland-sourced DOM has important effects on downstream DOM biodegradability even in catchments where upland area is substantially larger than peatland area.     

Lysimeter soil water balance evaluation for an experiment developed in the Southern Brazilian Atlantic Forest region

This study aims at monitoring the behaviour of the rainfall, runoff, drainage, soil water storage, and evapotranspiration variables involved in the water balance measured by lysimeter data. The evaluation of the water balance considered different time scales, where the components were monitored daily and in 10‐day accumulated period intervals. The results demonstrated that in wet periods the soil water content was greater at a depth of 10 cm, whereas in the dry periods a greater concentration was observed at 70 cm depth. At the depth of 30 cm, the lowest values of soil water content were observed for both wet and dry periods. The results, obtained through the use of tensiometers and time domain reflectometry installed internally and externally to the lysimeter, were very close, which was more noticeable during the periods of lower water loss by the soil. The water balance, calculated from the lysimeter data, demonstrated that 70% of the total rainfall was lost by the process of evapotranspiration. The drainage accounted for 27·5% of the precipitated water, highlighting the fact that this component should not be disregarded in the water balance calculation. Copyright © 2011 John Wiley & Sons, Ltd.     

Aquifer recharge from flash floods in the arid environment: A mass balance approach at the catchment scale

Estimation of the infiltration/natural recharge to groundwater from rainfall is an important issue in hydrology, particularly in arid regions. This paper proposes the application of The Natural Resources Conservation Service (NRCS) mass balance model to develop infiltration (F)–rainfall (P) relationship from flash flood events. Moreover, the NRCS method is compared with the rational and the Ф-index methods to investigate the discrepancies between these methods. The methods have been applied to five gauged basins and their 19 sub-basins (representative basins with detailed measurements) in the southwestern part of Saudi Arabia with 161 storms recorded in 4 years. The F–P relationships developed in this study based on NRCS method are: F = 39% P with R² = 0.932 for the initial abstraction factor, λ = 0.2. However, F = 77% P with R² = 0.986 for λ = 0.01. The model at λ = 0.01 is the best to fit the data, therefore, it is recommended to use the formula at λ = 0.01. The results show that the NRCS model is appropriate for the estimation of the F–P relationships in arid regions when compared with the rational and the Ф index methods. The latter overestimates the infiltration because they do not take λ into account. There is no significant difference between F–P relationships at different time scales. This helps the prediction of infiltration rates for aquifer recharge at ungauged basins from monthly and annual rainfall data with a single formula.     

Hydrological impacts of climate change predicted for an inland lake catchment in Ontario by using monthly water balance analyses

Potential hydrological impacts of climate change on long‐term water balances were analysed for Harp Lake and its catchment. Harp Lake is located in the boreal ecozone of Ontario, Canada. Two climate change scenarios were used. One was based on extrapolation of long‐term trends of monthly temperature and precipitation from a 129‐year data record, and another was based on a Canadian general circulation model (GCM) predictions. A monthly water balance model was calibrated using 26 years of hydrological and meteorological data, and the model was used to calculate hydrological impact under two climate change scenarios. The first scenario with a warmer and wetter climate predicted a smaller magnitude of change than the second scenario. The first scenario showed an increase in evaporation each month, an increase in catchment runoff in summer, fall and winter, but a decrease in spring, resulting in a slight increase in lake level. Annual runoff and lake level would increase because the precipitation change overrides evaporation change. The second scenario with a warmer, drier climate predicted a greater change, and indicated that evaporation would increase each month, runoff would increase in many months, but would decrease in spring, causing the lake level to decrease slightly. Annual runoff and lake level would decrease because evaporation change overrides precipitation change. In both scenarios, the water balance changes in winter and spring are pronounced. Copyright © 2009 John Wiley & Sons, Ltd.     

The relative contributions of alpine and subalpine ecosystems to the water balance of a mountainous,headwater catchment

Climate change is affecting the hydrology of high‐elevation mountain ecosystems, with implications for ecosystem functioning and water availability to downstream populations. We directly and continuously measured precipitation and evapotranspiration (ET) from both subalpine forest and alpine tundra portions of a single catchment, as well as discharge fluxes at the catchment outlet, to quantify the water balance of a mountainous, headwater catchment in Colorado, USA. Between 2008 and 2012, the water balance closure averaged 90% annually, and the catchment ET was the largest water output at 66% of precipitation. Alpine ET was greatest during the winter, in part because of sublimation from blowing snow, which contributed from 27% to 48% of the alpine, and 6% to 9% of the catchment water balance, respectively. The subalpine ET peaked in summer. Alpine areas generated the majority of the catchment discharge, despite covering only 31% of the catchment area. Although the average annual alpine runoff efficiency (discharge/precipitation; 40%) was greater than the subalpine runoff efficiency (19%), the subalpine runoff efficiency was more sensitive to changes in precipitation. Inter‐annual analysis of the evaporative and dryness indices revealed persistent moisture limitations at the catchment scale, although the alpine alternated between energy‐limited and water‐limited states in wet and dry years. Each ecosystem generally over‐generated discharge relative to that expected from a Budyko‐type model. The alpine and catchment water yields were relatively unaffected by annual meteorological variability, but this interpretation was dependent on the method used to quantify potential ET. Our results indicate that correctly accounting for dissimilar hydrological cycling above and below alpine treeline is critical to quantify the water balance of high‐elevation mountain catchments over periods of meteorological variability. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimation of evapotranspiration and its components from an apple orchard in northwest China using sap flow and water balance methods

Field experiments were conducted to investigate the effects of leaf area index and soil moisture content on evapotranspiration and its components within an apple orchard in northwest China for 2 years. Evapotranspiration in the non‐rainfall period was estimated using two approaches: the soil water balance method based on tube‐type time‐domain reflection measurements, and sap flow plus micro‐lysimeter methods. The two methods were in good agreement, with differences usually less than 10%. The components of evapotranspiration varied with canopy development. During spring and autumn, soil evaporation was dominating as result of low leaf area index. In summer, plant transpiration became significant, with an average transpiration to evapotranspiration ratio of 0·87. The crop coefficient K_c showed a strong linear dependence on leaf area index. The water stress coefficient K_s was around 1·0 when soil moisture was above 23% and started to decrease linearly after that. This study demonstrates that prediction of evapotranspiration in apple orchards can be made using the Food and Agriculture Organization's crop coefficient method from commonly available meteorological data in the area. Copyright © 2006 John Wiley & Sons, Ltd.     

Groundwater flushing of solutes at wetland and hillslope positions during storm events in a small glaciated catchment in western New York,USA

While the role of groundwater in flushing of solutes has long been recognized, few studies have explicitly studied the within‐event changes in groundwater chemistry. We compared the changes in groundwater chemistry during storm events for a wetland and hillslope position in a small (1·5 ha) glaciated, forested catchment in western New York. Flushing responses for dissolved organic carbon (DOC) and nitrogen (DON), nitrate (NO₃) and sulfate (SO₄) in wetland and hillslope groundwaters were also compared against the corresponding responses in stream water. Eight storm events with varying intensity, amount, and antecedent moisture conditions were evaluated. Solute flushing patterns for wetland and hillslope groundwaters differed dramatically. While DOC concentrations in wetland groundwater followed a dilution trend, corresponding values for hillslope groundwater showed a slight increase. Concentrations for NO₃ in wetland groundwater were below detection limits, but hillslope groundwaters displayed high NO₃ concentrations with a pronounced increase during storm events. Flushing responses at all positions were also influenced by the size of the event and the time between events. We attributed the differences in flushing to the differences in hydrologic flow paths and biogeochemical conditions. Flushing of the wetland did appear to influence storm‐event stream chemistry but the same could not be said for hillslope groundwaters. This suggests that while a variety of flushing responses may be observed in a catchment, only a subset of these responses affect the discharge chemistry at the catchment outlet. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterizing the climatic water balance dynamics and different runoff components in a poorly gauged tropical forested catchment,Nicaragua

ABSTRACT

The water balance dynamics and runoff components of a tropical forested catchment (46?km²) on the southwestern Pacific coast of Nicaragua were studied combining hydrometry, geological characterization and hydrochemical and isotopic tracers (three-component hydrograph separation). The climatic water balance was estimated for 2010/11, 2011/12 and 2012/13 with net values of 811?mm year^-1, 782?mm year^-1 and –447?mm year^-1, respectively. Runoff components were studied at different spatial and temporal scales, demonstrating that different sources and temporal contributions are controlled by dominant landscape elements and antecedent rainfall. In forested sub-catchments, permeable soils, stratigraphy and steep slopes favour subsurface stormflow generation contributing 50% and 53% to total discharge. At catchment scale, landscape elements such as smooth slopes, wide valleys, deeper soils and water table allow groundwater recharge during rainfall events. Groundwater dominates the hydrograph (50% of total discharge) under dry prior conditions. However, low soil infiltration capacity generates a larger surface runoff component (42%) under wet prior conditions which dominates total discharge. Our results show that forested areas are important to reduce surface runoff and thus soil degradation, which is relevant for the design of water management plans.

Editor D. Koutsoyiannis Associate editor D. Gerten